The present invention relates to a lens tube retraction mechanism for a camera having a lens tube which is slidable relative to the body of the camera between a photographing position and a retracted position and more particularly to a lens tube retraction mechanism capable of retracting and projecting a retractable lens tube smoothly and lightly while the lens tube supporting capability is increased when the lens tube is projected to the photographing position.
Conventionally, various lens tube retraction mechanisms have been proposed, such as a type moving a pusher lever upwards quickly by a roller which is engaged with a lens tube, a type moving a wedge upwards quickly by a roller, a bayonet type and a link type.
Referring to FIGS. 1 and 2, there is shown a conventional lens tube retraction mechanism of the type moving a pusher lever upwards by a roller.
As can be seen from FIGS. 1 and 2, the same members of the lens tube retraction mechanism are symmetrically disposed on the opposite sides of the camera. However, for simplification and convenience of explanation only, the members disposed on one side of the camera will be explained hereinafter.
In FIGS. 1 and 2, transverse grooves 21g and 21h are formed in opposite side walls of a lens tube guide frame 21 which is disposed inside a camera body 1. The shaft portions of a pair of rollers 41 are arranged so that each shaft portion passes through the transverse grooves 21g and 21h and is engaged with a lens tube support member 2b of a lens tube 2 which is disposed inside the lens tube guide frame 21. The shaft portion of each roller 41 is fitted into a slot 4a formed in one end portion of each of a pair of intermediate levers 4. A projected portion 8b of a pusher lever 8 which is situated above the roller 41 is engaged with the roller 41, and the pusher lever 8 is urged downwards by coil springs 83, guided by slots 8e formed in the pusher lever 8, so that the lens tube 2 can be selectively positioned at either a projected position or a retracted position by the intermediate levers 4 which are respectively linked with a retraction operation lever 32 of the lens tube 2.
In this retraction mechanism, when the lens tube 2 is retracted from the projected photographing position to the retracted position by pushing the intermediate lever 4 inwards through the retraction operation lever 32, the intermediate lever 4 pushes the lever 8 upwards. However, since no force other than a frictional force is applied to the roller 41, the position of the roller 41 in the slot 4a of the intermediate lever 4 is indefinite and, accordingly, the roller 41 is not always at one extreme end of the slot 4a. Furthermore, it may occur that the shaft portion of each roller 41 is not in the same position within the slot 4a of each intermediate lever 4. In other words the two intermediate levers 4 may be in different positions in relation with the opposite rollers 41. If the retraction operation is performed while the two intermediate levers 4 are in different positions, different forces are applied to the lens tube 2 from the opposite sides thereof so that the lens tube 2 is tilted, which keeps the retraction operation from being smooth.
Furthermore, as mentioned previously, when the lens tube 2 is retracted from the photographing position to the retracted position by pushing the intermediate levers 4 inwards through the retraction operation levers 32, each intermediate lever 4 pushes the lever 8 upwards. In this case, when the force necessary for moving the pusher lever 8 upwards is reduced by weakening the resilient force of the coil springs 83, the lens tube supporting capability is reduced and the lens tube 2 cannot be fixed securely, so that the position of the lens tube 2 cannot be determined securely and accurately. Thus may tilt the lens tube 2 in the lens tube guide frame 21, causing one side of a photograph to become out of focus. On the other hand, when the lens tube supporting capability is increased by means of stronger springs 83, the retraction operation becomes heavy and difficult.
Referring to FIG. 3, there is schematically shown part of the lens tube retraction mechanism of the type of moving a wedge upwards by a roller. In FIG. 3, when a front cover 3 is closed, the intermediate lever 4 rotates a wedge lever 9 counterclockwise about a shaft 91 and, at the same time, a pin 46 which is engaged with the lens tube 2 is caused to slide within the transverse groove 21g. In this lens tube retraction mechanism, the mechanical construction must be such that the strength of the retraction mechanism is sufficient to protect the mechanism against having a great outer force applied thereto. Therefore, the mechanism becomes complex, and precision parts are necessary. Furthermore, in a bayonet type of mechanism projection and retraction of the lens tube cannot be performed by one-touch operation. The link type of mechanism also has the same shortcoming as the bayonet type.